During semiconductor device processing, metal interconnects can act as either anodes or cathodes of a photovoltaic cell formed in a semiconductor substrate. In the presence of an electrolyte, which occurs during chemical mechanical processing (CMP), electrical current can flow in the photovoltaic cell and causing electrolysis at the surface. Metal interconnects can be oxidized at anodic sites forming ions that may be transported and reduced at cathodic sites. The deposited metal that is reduced at the cathode may grow and form a dendrite. If the dendrites are large enough, they may extend between multiple metal regions and may short the metal regions together. This can cause both yield and reliability problems.
One solution to minimize dendrites is to alter the chemistry of the solutions used during CMP and post-CMP cleaning. While such solutions can be successful in reducing the number of dendrites at the cathodes, they may fail to prevent voids from forming at the anodes. In other words, they fail to prevent current from flowing between the anode and cathode regions.
An approach to minimize electrolysis (i.e., dendrite formation) and corrosion is to polish and scrub wafers in darkness to prevent carrier photogeneration. However, polishing of semiconductor wafers in a dark or dim environment may create difficulties for operators and engineers to see, which increases the risk of accidents.
To enable operators and engineers to see while still minimizing dendritic growth, the windows of CMP tools and/or post-CMP cleaning tools can be covered with a dark or opaque material to prevent light from hitting the wafer when it is wet. However, the dark material on the CMP tools and/or post cleaning tools prevents operators and engineers from viewing the wafer during processing to determine if, for example, a semiconductor wafer has stopped processing or the polishing solution has stopped flowing for unknown reasons. Furthermore, if for some reason it is necessary for the wafer to be removed (e.g., if processing stops because the semiconductor wafer is stuck in the CMP tool), once the door of the CMP tool is opened, dendrites will grow and the semiconductor wafer may suffer reliability problems or yield loss. Therefore, a need exits to overcome the problems of the above processes used to try to minimize dendritic growth.
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